This invention relates to low-E coated articles that have approximately the same color characteristics as viewed by the naked eye both before and after heat treatment (e.g., thermal tempering), and corresponding methods. Such coated articles may be used in insulating glass (IG) units, windshields, and other suitable applications.
Solar control coating systems are known. For example, commonly owned U.S. Pat. No. 5,688,585 discloses a solar control coated article including: glass/Si3N4/NiCr/Si3N4. One object of the ""585 patent is to provide a sputter coated layer system that after heat treatment is matchable colorwise with its non-heat treated counterpart. While the coating systems of the ""585 patent are excellent for their intended purposes, they suffer from certain disadvantages. In particular, they tend to have rather high emissivity values (e.g., because no silver (Ag) layer is disclosed in the ""585 patent).
Low-emissivity (low-E) coating systems are also known in the art. For example, commonly owned U.S. Pat. No. 5,376,455 discloses: glass/Si3N4/NiCr/Ag/NiCr/Si3N4. Low-E coating systems such as this are typically designed for maximum visible transmission. For this reason, the NiCr layers are made rather thin. This enables high transmission and low-E characteristics, but less than desirable solar control (e.g., shading coefficient) characteristics. Thus, the low-E coating system of the ""455 patent is unfortunately not sufficiently color matchable after heat treatment with its non-heat treated counterpart, and lacks superior solar control characteristics such as shading coefficient (SC).
Accordingly, when it is desired to provide an insulating glass (IG) unit with both low emissivity (low-E) and solar control characteristics, it has often been necessary to combine the solar control coating of the ""585 patent with the low-E coating of the ""455 patent in a single IG unit. For example, the solar control coating of the ""585 patent is placed on the #2 surface of the IG unit while the low-E coating of the ""455 patent is placed on the #3 surface of the IG unit. The need for these two separate and distinct coatings in an IG unit is undesirable, for both cost and processing reasons.
The need for matchability (before heat treatment vs. after heat treatment) is also known. Glass substrates are often produced in large quantities and cut to size in order to fulfill the needs of a particular situation such as a new multi-window and door office building, vehicle windshield needs, etc. It is often desirable in such applications that some of the windows and/or doors be heat treated (i.e., tempered, heat strengthened or bent) while others need not be. Office buildings often employ IG units and/or laminates for safety and/or thermal control. It is desirable that the units and/or laminates which are heat treated substantially match their non-heat treated counterparts (e.g., with regard to color, reflectance, and/or the like, at least on the glass side) for architectural and/or aesthetic purposes. In addition, it is sometimes desirable that certain windows, doors, windshields, etc. be of a substantially neutral color, preferably tending to the blue-green side of the spectrum.
It has in the past been possible to achieve matchability in systems other than those of the aforesaid ""585 patent, but only between two different layer systems, one of which is heat treated and the other is not. The necessity of developing and using two different layer systems to achieve matchability creates additional manufacturing expense and inventory needs which are undesirable.
U.S. Pat. Nos. 6,014,872 and 5,800,933 (see Example B) disclose a heat treatable low-E layer system including: glassTiO2/Si3N4/NiCr/Ag/NiCr/Si3N4. Unfortunately, when heat treated this low-E layer system is not approximately matchable colorwise with its non-heat treated counterpart (as viewed from the glass side). This is because this low-E layer system has a xcex94Eab* (glass side) value of greater than 4.1 (i.e., for Example B, xcex94a*G is 1.49, xcex94b*G is 3.81, and xcex94L* is not measured; using Equation (1) below then xcex94E on the glass side must necessarily be greater than 4.1 and is probably much higher than that).
In view of the above, it will be apparent to those skilled in the art that there exists a need for a coating or layer system that could satisfy both solar control and low-E requirements (e.g., so a solar control coating and a separate low-E coating need not be used together on different surfaces of the same IG unit). In addition to and/or instead of the above need, there also exists a need in the art for a low-E coating or layer system which after heat treatment substantially matches in color and/or reflection (as viewed by a naked human eye from the glass side) its non-heat treated counterpart. In other words, there exists a need in the art for a low-E matchable coating or layering system.
It is a purpose of this invention to fulfill any and/or all of the above-listed needs, and/or other needs which will become more apparent to the skilled artisan once given the following disclosure.
An object of this invention is to provide a low-E coating or layer system that has good color stability with heat treatment.
Another object of this invention is to provide a low-E matchable coating or layering system.
Another object of this invention is to provide a coating or layer system that has improved IR reflectance characteristics relative to those of the coating systems described in U.S. Pat. No. 5,688,585.
Another object of this invention is to provide a coating or layer system that when heat treated is substantially matchable to its non-heat treated counterpart.
Another object of this invention is to fulfill one or more of the above-listed objects.
It has been surprisingly found that silver in rather substantial thicknesses may be employed while still achieving color stability with heat treatment (e.g., thermal tempering, bending, or heat strengthening). The layer systems of the invention may be utilized, for example, in the context of IG units, vehicle windows and windshields, or the like.
According to certain exemplary embodiments of this invention, one or more of the above-listed objects or needs is/are fulfilled by providing a coated article comprising:
a layer system supported by a glass substrate, said layer system comprising an infrared (IR) reflecting silver layer located between first and second dielectric layers; and
wherein said coated article has a xcex94E*ab value (glass side) no greater than 3.0 (more preferably no greater than 2.5) after or due to heat treatment.
Further embodiments of this invention fulfill one or more of the above-listed needs or objects by providing a coated article comprising:
a substrate;
a layer system provided on the substrate, said layer system comprising from the glass outwardly, a first silicon nitride inclusive layer, a first Ni or NiCr inclusive layer, an IR reflecting metal layer, a second Ni or NiCr inclusive layer, and a second silicon nitride inclusive layer;
wherein each of said first and second Ni or NiCr inclusive layers is at least about 20 xc3x85 thick; and
wherein said coated article has a hemispherical emissivity (Eh) of no greater than 0.25 before heat treatment, a sheet resistance RS no greater than 20 ohms/square before heat treatment, and a xcex94E*ab value (glass side) no greater than 2.5 after or due to heat treatment.
Other embodiments of this invention fulfill one or more of the above-listed needs or objects by providing a method of making a coated article, the method comprising:
depositing a layer system on a glass substrate, the layer system including an infrared (IR) reflecting metal layer located between first and second dielectric layers, wherein prior to heat treatment the glass substrate with the layer system thereon has a sheet resistance RS no greater than 20 ohms/square; and
heat treating the substrate with the layer system thereon so that due to said heat treating the resulting substrate with the layer system thereon has a xcex94E*ab value (glass side) no greater than 2.5.